Many bubble deniers point to average prices for the country as a whole, which look worrisome but not totally crazy. When it comes to housing, however, the United States is really two countries, Flatland and the Zoned Zone.
In Flatland, which occupies the middle of the country, it’s easy to build houses. When the demand for houses rises, Flatland metropolitan areas, which don’t really have traditional downtowns, just sprawl some more. As a result, housing prices are basically determined by the cost of construction. In Flatland, a housing bubble can’t even get started.
But in the Zoned Zone, which lies along the coasts, a combination of high population density and land-use restrictions - hence “zoned” - makes it hard to build new houses. So when people become willing to spend more on houses, say because of a fall in mortgage rates, some houses get built, but the prices of existing houses also go up. And if people think that prices will continue to rise, they become willing to spend even more, driving prices still higher, and so on. In other words, the Zoned Zone is prone to housing bubbles.
And Zoned Zone housing prices, which have risen much faster than the national average, clearly point to a bubble.